Machines for the automatic sharpening of broaching or reaming tools of the general type described above, having a scanning device and a scanning finger, are known from U.S. Pat. No. 3,646,593 and are also available on the market. In these known machines, when there is an appropriate movement of the horizontal slide the scanning finger drops via the cutting edge of the reaming tooth of a broaching or reaming tool which is to be ground, and the horizontal slide is thus arrested. A radial advancement of the vertical slide having the grinding slide then occurs as well, in accordance with the vertical deflection of the scanning finger, which is resting with its horizontal scanning face on the free face of the reaming tooth. When the grinding slide having a grinding spindle is radially advanced in this manner, the scanning finger is raised from its scanning position in contact with the tooth, and the grinding disc is guided a plurality of times over the face to be ground, in accordance with an appropriately predetermined positioning. The next tooth is then ground. Because wear marks are often found on the worn cutting edge of a reaming tooth, that is, the edge which is now to be ground, and these marks cause errors in ascertaining the actual position of the cutting edge on the part of the scanning finger, an undercut is provided in front of the flat scanning face, so that the horizontal scanning face or rather its forward edge, defined by the undercut, rests on the free face of the tooth spaced apart from the cutting edge by a distance such that there are no further wear marks or the like. The face of the undercut along which the scanning finger drops downward via the worn cutting edge extends vertically. Machines of this general type for the automatic sharpening of broaching or reaming tools have become widely established and have proved themselves in practice.
However, it has been found in practice that very frequently, wear marks which cause errors in ascertaining the set-point position of the cutting edge also exist on the cutting face in the vicinity of the cutting edge. A further particularly important point is that naturally the worn edge is no longer a sharply defined edge, but rather an arc-like, curved face, so that errors in scanning occur. For this reason, it is efficacious to scan not only the free face but also the cutting face, at a predetermined distance from the location of the original, unworn cutting edge.
With respect to the above problem, it has become known from German laid-open application DE-OS No. 29 26 807 to use two scanning fingers, one of which scans the free face while the other scans the cutting face. This embodiment may be satisfactory in functional terms; however, because two scanning fingers have to be provided, it is expensive to build and also correspondingly more delicate.